As an optical disk permitting writing of information, there are a CD-R (CD-Recordable) and a CD-RW (CD-Rewritable) for a CD standard, and a DVD-R, a DVD-RW, a DVD+R, a DVD+RW and a DVD-RAM for a DVD standard. For example, a groove is cut in a CD-RW disk substrate with a sine wave shape or the like. The part of a recording layer corresponding to the groove is a recording track. The serpentine of the groove is called as a wobble. To the wobble, FM-modulated positional information, that is, time axis information showing an absolute position on a disk, is written as an ATIP (Absolute Time in Pre-groove) signal.
The ATIP signal is written so that its frequency become 22.05 kHz±1 kHz when an optical disk rotates at a predetermined speed, for example, at a standard speed. One sector of the ATIP signal corresponds with one data sector (2352 bytes) of writing data. When the writing data is written, the writing is performed while synchronizing the sector of the ATIP signal with the data sector of the writing data.
FIG. 1 shows the frame structure of an ATIP signal. One frame has 42 bits including first 4-bit SYNC, 24-bit time axis information (minutes, seconds, frame numbers, each for 8 bits), and 14-bit CRC (Cyclic Redundancy Code) as an error detecting code. A CD-RW writing and reading device performs rotational control of the disk, that is, the spindle servo based on the SYNC of the ATIP signal.
In such the writing and reading device, interference elements such as scratch, dirt and fingerprint on a recording surface, mechanical characteristic fluctuation (eccentricity, eccentricity of center of gravity, skew and wobbling), electric characteristic fluctuation (degraded S/N and reflectivity fluctuation), and vibration and shock from outside affect reading of the above ATIP signal. In particular, in recent years, the data writing and reading speeds to and from an optical disk have been increased dramatically. The influence of the interference elements upon the reading of the ATIP signal has been enlarged more and more. When a reading error of the ATIP signal occurs, the spindle servo is unstable. Degradation of the reading characteristic (seek time and transfer rate) and deterioration of the writing characteristic occur. In the worst case, there are problems of disabled writing and reading and occurrence of a writing error.